Office equipment such as printers, scanners, copiers and facsimile machines are in universal use. Recently, new types of office equipment have been introduced, which combine functions of various machines into a single piece of equipment. These multi-purpose machines include, for example, the "OfficeJet" series of machines marketed by Hewlett-Packard Company, which includes functions of a printer and a facsimile machine. One characteristic of many of these multi-function machines is the use of two input media sources, with a drive to pick a sheet of media such as paper from one of the input sources and pass the picked sheet through a shared media path. For example, the machine may include an optical scanner and a printing apparatus, such as a scanning carriage holding an ink-jet print cartridge for example, disposed along a common media path through the machine. One input media source can be for holding documents to be scanned by the optical scanner, and the other media source can be for holding a supply of blank paper for printing. In one mode of operation, document sheets are sequentially fed from the first input source into the shared media path and past the scanning apparatus for optical scanning. In another mode of operation, blank sheets are fed from the second input source into the shared media path and to a printing area for printing by the printing apparatus. The drive apparatus can include a gear train for selectively driving apparatus to pick a sheet from one of the input sources.
One type of drive system employs a solenoid to determine which of three states the gear train will shift into. The first state is the state in which an input gear is engaged with a first gear which drives the automatic document feeder. The second state is the state in which the input gear is in a neutral position, and drives neither the first gear nor a second gear. The third state is the state in which the input gear is engaged with the second gear which drives the automatic sheet feeder. The input gear is mounted on a swing arm with a drag clutch. When the input gear is being driven backwards, the swing arm (motivated by the driving friction) swings back until it is in engagement with the first gear. The solenoid is attached to a lever, which, when the solenoid is not energized, is in a position such that when the input gear and associated drag from the drag clutch is driven forward, the swing arm is driven forward until it hits the lever. This position thus defines the neutral position where the drive gear is mated with neither the first or second drive gear. The solenoid is energized when the input gear is being driven forward, which removes the lever from the input gear swing arm's path, allowing the input gear to move fully into engagement with the second gear.
There are several problems with the solenoid selection of the state of the drive gear train. There is a force hierarchy that needs to exist for all operating conditions and consideration for age and wear of the mechanism. If the solenoid spring is not strong enough to overcome the drag force of the input gear swing arm, the swing arm will push the solenoid lever aside and engage with the second gear instead of remaining in a neutral state. If, on the other hand, the solenoid spring is too strong, the solenoid will not be able to overcome the spring and rotate the solenoid lever when it is intended to have the input gear swing arm engage with the second gear.
The solenoid is force limited due to cost, space and power requirements. A solenoid is a significant cost factor in a consumer product, particularly when considering the electronic drive components and additional power supply capacity need to drive the solenoid. Moreover, the manufacturing tolerances of solenoids result in radically different characteristics from solenoid to solenoid, particularly troubling when coupled with the force hierarchy requirements. Additional disadvantages of a solenoid include the heat generated by the solenoid.
It would therefore represent an advance in the art to provide a technique for providing a multistate switching technique for the input drive of an office machine which does not include a solenoid actuator.